I. Field of the Invention:
This invention relates generally to digital data processing apparatus, and more specifically to a system for the mass replication of information (software) stored on a recording medium, e.g., magnetic disks.
II. Discussion of the Prior Art:
With the advent of the personal computer and the small business computer, there has been a significant growth in the marketing of packaged software products where floppy disks are used as the storage medium. This rapid growth has resulted in the need for equipment capable of high volume duplication of information-bearing floppy disks. While the personal computers and small business computers can be used to make copies of programs which are not copy-protected, it is necessarily done on a slow, one-at-a-time basis which is too inefficient for firms engaged in software publication. There is on the market a system referred to as the Formaster Disk Duplicator, which is a product of the Formaster Corporation of San Jose, Calif., which has been designed to facilitate the mass duplication of software on floppy disk media. That system incorporates a relatively large random access memory to store data from a diskette being copied. A plurality of floppy disk drives are coupled through associated controller modules to a control processor. Operating under software control, then, the diskette to be copied is first read and the information is stored in the system's RAM. Upon command, that data is transmitted through the systems's controllers to the disk drives, each of which incorporates a buffer memory for temporarily storing the data patterns to be recorded on the diskette. Each of the drives operates asynchronously relative to the other drives in the system. Each of the drives, however, has a means for generating an index or reference mark and, when that mark passes an appropriate sensor, the data contained within the drive's buffer is written on to the diskette. In that each of the drives must wait until its own index mark reaches a predetermined location before the actual write operation can take place, there can be a signifcant loss of time and, therefore, output capacity. Furthermore, the need to incorporate buffer memories in each of the drives for temporarily holding data to be recorded tends to be expensive.
In a co-pending patent application of Ronald R. Johnson, et al, Ser. No. 625,781, filed June 28, 1984, and entitled, FLEXIBLE DISKETTE COPY/FORMATTING SYSTEM, there is described an apparatus for copying and duplicating flexible magnetic storage diskettes, commonly referred to as floppy disks.
The present invention may be incorporated into the system described in the Johnson, et al application and provides a means whereby each of a large plurality of slave drives may be brought into rotational synchronization with a master index such that when this synchronization is achieved, the data to be replicated may be transmitted from the master to all of the slaves simultaneously and recorded on-the-fly whereby the need for large buffer memories for storing the recorded data until an internally generated index pulse is sensed can be eliminated.
In accordance with the invention, each of the plural slave units includes a motor for rotating a magentic storage disk at a speed determined by a suitable control circuit. The disk driven by the slave drive will typically have an index mark in the form of a hole or a recorded spot which acts to generate an index pulse once for each revolution of the disk. Otherwise, the drive's spindle may include an index pulse generator. In accordance with the present invention, an additional circuit is used to influence the motor control circuit of the drive itself. That is to say, each of the slave units includes a so-called "sync board" whose electronic circuits create an analog signal for adjusting an element on the motor control circuit associated with the drive.
In addition to its ability to transfer data and control signals over a communications link to the plural slave units, a crystal controlled oscillator in the master also generates and transmits a so-called "sync pulse" which comprises a reference or index. This "sync pulse" is also transmitted over the communications link to each of the slave units, and the "sync board" circuitry then develops the requisite analog signal for adjusting the speed of the drive motor so that the index pulse produced by each of the slaves is forced into synchronism with the sync pulse sent from the master. Located on the sync board is circuitry which functions to compare the time of occurrence of the master sync pulse relative to the occurrence of the Drive Index from the slave. In one form of the invention, it comprises a counter which is enabled by the occurrence of the Sync Index from the master and which then accumulates regularly occurring clock pulses until such time as the slave produces its Drive Index. The output from the counter circuit then represents a displacement error and this digital quantity is sent to a decode circuit which functions to generate timing pulses at a rate corresponding to the time difference between the occurrence of the Sync Index from the master and the disk index from the slave. Accordingly, the greater the angular displacement between the Master Index and the Slave Index, the greater the number of timing pulses. These timing pulses are accumulated in a counter whose output feed a digital-to-analog converter. It is the output of the D/A converter which, in turn, adjusts the speed of the slave's drive motor.
To detect when synchronization is achieved and when once achieved synchronization is later lost, a so-called "window's generator" is included on the sync board associated with each of the slave drives. So long as the Disk Index falls within a prescribed window, the slave is said to be in synchronism with the master. Loss of synchronization may be detected and that event reported back over the communications link to the master whereby, under software control, appropriate corrective action may be initiated.
In accordance with an alternative arrangement, rather than employing plural drives having DC motors therein, AC synchronous motors may be employed which, of course, operate at a speed directly related to the frequency of the power applied to the motors. In accordance with the alternative embodiment, then, the plural disk drive units driven by hysteresis synchronous motors are synchronized relative to a selected reference point derived from the AC supply voltage cycle. Once synchronization is achieved, the programming information and data contained on the master's diskette drive can be broadcast to all of the plural slave units and written on-the-fly, again obviating the need for expensive and time-consuming buffers.